The present invention relates generally to invasive probes for therapeutic purposes and, more particularly, to invasive probes and related methods for hyperthermia treatment and ablation of body tissue.
Probes configured for generally localized radiation of electromagnetic energy at radio frequencies, i.e., RF energy, have been beneficially used to heat body tissue for therapeutic purposes. Typically, a probe is positioned in proximity to the target tissue via insertion through a small incision. One such purpose is in the treatment of cancerous tumors, which are particularly susceptible to damage at elevated temperatures resulting from exposure to RF energy. The application of sufficient energy will result in necrosis of the tumor, e.g., necrosis of cancerous tumor cells generally occurs once heated above a certain temperature threshold (about 50 to 55 degrees Celsius). For other purposes, such as in various hyperthermia treatments, a lower temperature threshold is typically used. Nonetheless, for a probe to be effective, it must radiate sufficient energy to raise the temperature of the target tissue above the prescribed temperature threshold.
However, viable tissue neighboring the target tissue can be damaged by excessive heating through overexposure to RF energy. In some therapeutic applications beneficial results can still be achieved even with relatively significant incidental damage to viable tissue. Although, in certain therapeutic applications, even minimal damage to viable tissue can result in grave harm to the patient, e.g., in the treatment of brain tumors. Thus, for an RF probe treatment to be permissible in certain applications, the probe must be able to deliver sufficient localized energy to effect necrosis of the tumor while minimizing damage to viable tissue. With the benefits of an MRI machine, detailed information about the target tumor can be obtained such as its position, orientation, shape, and volume. Frequently, tumors have a generally spherical shape. Traditional probe designs have been generally effective in certain applications, but, in other applications, the risk of damage to viable tissue has been too great for them to be a practical treatment option, particularly if a precise zone of therapeutic effectiveness is needed.
It is, therefore, an object of this invention to provide an improved probe configured to generate a predetermined zone of therapeutic effectiveness having a selected geometry and volume, to include substantially spherical shapes, for use in heating a target region of tissue such as in hyperthermia treatment and ablation of tumors.
Other objects of this invention include making the probe low cost so it can optionally be disposed after a single use and configuring the probe to allow MRI imaging to discern the probe placement and position without unduly interfering with image quality.
These and other objects of the invention will be understood more particularly from the following description taken in conjunction with the accompanying drawings.
An invasive probe assembly is provided for application of RF energy to a volume of body tissue. The probe assembly includes an RF source configured to provide an RF energy having selected characteristics, a probe having a probe shaft and an antenna positioned therein, and a feed line for providing conductivity from the RF source to the antenna probe. The probe assembly is adapted to generate a zone of therapeutic effectiveness having a selected geometry and volume.
The antenna preferably is a dipole antenna having a first dipole region located at the distal end of the probe shaft and a second dipole region located proximate thereto along the probe shaft. A choke having selected characteristics to inhibit excessive current flow back and excessive heating of the feed line is preferably located at the second dipole region.
The invention also resides in a method of heating body tissue for a therapeutic purpose. In this method, a probe assembly, including a probe with an antenna, an RF source, and a feed line, is used. The method includes positioning the probe in a selected location with reference to a target tissue, initiating an electromagnetic field from the antenna having a selected geometry, and producing a zone of therapeutic effectiveness having a selected geometry and volume.
The producing step preferably includes, taking periodic temperature measurements from sensors positioned at a selected location, and manipulating the selected characteristics of the RF energy to include duration and/or power level.
The invention further resides in a method of making an invasive probe having a dipole antenna and a feed line adapted to connect the dipole antenna to an RF source. The method comprises fitting an insulator having selected characteristics over the feed line at a selected location along the feed line; and fitting a radiating sleeve having selected characteristics over the dielectric sleeve and the feed line such that the sleeve is connected to an outer conductor of the feed line at a distal end and left open at a proximate end, thereby forming a choke.
Other features and advantages of the invention should become apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.